实例之间的差异

Question

been messing around with JFrames a bit, and I noticed something:

JFrame frame = new JFrame();

Works, from what I can tell, the exact same as:

JFrame frame = JFrame.class.newInstance();

Are there any differences between these two ways when just using the Default instance with no parameters?

Thanks,

Legend

Answer 1

The newInstance() method in java.lang.Class constructs an instance of the class using the no-argument contructor -- so no, the two JFrame s would be identical.

The Class.newInstance() method becomes important when the Class object is created using a class name at runtime -- for example, a class name read from a file. Then you can say

String theClassName = ...;
Class clazz = Class.forName(theClassName);
Object o = clazz.newInstance();

Now you have an instance of a class whose name was not known when this code was compiled. If you know (by convention) that the named class implements some interface or extends some class, then you can cast the Object to that interface or class, and use it that way. This is how, for example, servlet containers load servlets as described in configuration files, or web browsers load applets named in HTML.

Answer 2

参见http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#newInstance （）

Answer 3

newInstance() throws two checked exceptions that you have to deal with, and it prevents the compiler from telling you when you're doing something wrong (like trying to instantiate an abstract class).

And there's no such thing as a "Default instance."